NOx concentrations within the cylinder of an operating single-cylinder version of a passenger-car type, indirect-injection diesel engine have been measured using a total cylinder sampling system. This system utilizes an explosively actuated cutter to cut a diaphragm sealing the precombustion chamber. The cylinder charge is then rapidly cooled and diluted as it flows from the cylinder into a sampling bag. Pressure decay rates during blowdown range from 3000 to 6000 MPa s-1. This should be adequate to quench NOx reactions within a few crankangle degrees. The system has been used to determine in-cylinder NOx concentrations for eleven different operating conditions. Engine speeds of 1000 and 1500 RPM and the load range corresponding to equivalence ratios ranging from 0.32 to 0.94 were explored. The influences of fuel injection timing and exhaust gas recirculation were also examined. NOx concentrations rise rapidly after the onset of combustion and approach exhaust levels late in the expansion stroke. Peak NOx concentrations measured in the cylinder are as much as 15-20% greater than exhaust NOx concentrations. The experimental data were compared with model predictions made using MIT's stochastic combustion model for this engine. In general, the modeled results were in good agreement with the experimental results. The major difference was that the model did not predict higher NOx concentrations in the cylinder than in the exhaust.
Bibliographical noteFunding Information:
The research done at the University of Minnesota was supported by General Motors Research Laboratories. Their financial support and technical assistance is gratefully acknowledged. The contribution of Jim Myers in making the MIT code easy to use by non-modelers and the helpful discussions with Tanvir Ahmad and Alex Alikdas concerning the re-suits of the study are greatly appreciated. The authors also wish to thank Michael J. Pipho for his assistance in conducting the experiments and Betsy Antinozzi for her preparation of the manuscript.